Preparation And Study Of Particle Reinforced Metal Matrix Composites With High Thermal Conductivity For Electric Packaging

With the development of the third semiconductor instrument,thermal management in microelectronic technology has become more and more important.A new kind of materials with excellent thermo-physical properties which can still work at200 ^oC-600^oC is imminently needed.Pure copper（Cu）and silver（Ag）provided with higher thermal conductivity（401W/（m·K）and 429W/（m·K）respectively at room temperature）,higher melting point（1083.40^oC and 961.78^oC respectively）and lower coefficient of thermal expansion(16.5×10^-6/K and 19.2×10^-6/K respectively)than aluminium.SiC and diamond particles exhibited a high thermal conductivity and a low coefficient of thermal expansion are often used as reinforcement materials.Therefore,the use of SiC or Diamond particles as reinforcements in Cu or Ag matrix composites are considered to exhibit a high thermal conductivity,low coefficient of thermal expansion and excellent thermal physical properties and considered to be a new generation of thermal management materials.In this paper,firstly,Mo coating was successfully deposited on the surface of SiC and Diamond by magnetron sputtering method or sol-gel method,and the effects of the magnetron sputtering technics and the following crystallized heat-treatment on the surface morphology and the composition of Mo coating were studied in detail.Then,the hot-pressing sintering for Cu or Ag metal matrix composites were studied and optimized.The microstructure,thermal physical properties and mechanical properties of the Cu or Ag metal matrix composites were analysed in detail.At last,the model for the thermal conductivity of particle reinforced metal matrix composites was designed and calculated and validated according the results of the composites fabricated in this paper.Mo coating can be successfully deposited on the surface of SiC and Diamond by magnetron sputtering method,and the morphology and the composition of Mo coating are mainly determined by the power and temperature of the magnetron sputtering equipment.The original morphology of the Mo coating can not accumulate compactly and the Mo atoms are in amorphous state.The following crystallized heat-treatment is vital to improve the surface morphology of Mo coating.During the crystallized heat-treatment,with the temperature rose from 600^oC to 1200^oC,the morphology evolution of the Mo coating on SiC or Diamond particles was as follows:primary densification and crystallization of Mo coating,compact crystallization of Mo coating,dispersive accumulation of Mo coating,reaction with SiC or Diamond.Simutaneously,Mo atoms also evolute from amorphous Mo to crystalline Mo and finally stabilized as Mo compound（Mo₂C or MoSi₂）.The wetting angle between Cu and SiC minished form 149^o to 81^o,and the wetting angle between Cu and Diamond minished form 146^o to 83^o after surface modification,when the testing temperature is 1150℃.While the testing temperature is 1050℃,the wetting angle between Ag and SiC minished form141^o to 82^o,and the wetting angle between Ag and Diamond minished form 138^o to81^o after surface modification.Mo coating can be also successfully deposited on the surface of SiC particles by sol-gel method,and the best processing parameters are as follows:SiC/MoO₃=5/1（mass ratio）,H₂O₂/C₂H₅OH=1/1（volume ratio）.After restore treatment at 540^oC and940^oC for two steps,the coating changed from MoO₃ to MoO₂ first and then into Mo coating absolutely.The Mo coating includes double layers,and the bottom layer is continuous and uniformly and the upper layer is unconsolidated.The hot-pressing sintering for Cu matrix composites were studied and optimized.The densification process of SiC_p/Cu and Diamond_p/Cu is mainly affected by hot-pressing temperature,time and pressure.Compactness and hermeticity of the composites increased first and decreased later with the increase of hot-pressing temperature and time,and increased go ahead with the increase of hot-pressing pressure.However,the Cu matrix is easy to be forced out when the pressure and the temperature are too high.The best processing parameters of hot-pressing sintering are as follows:hot-pressing temperature 850^oC,hot-pressing time 120min,hot-pressing pressure 30Mpa.Compactness and hermeticity of the composites increased obviously after surface modification,and the magnetron sputtering method is better than the sol-gel method.The reinforced particles distribute evenly in the microstructure of SiC_p/Cu and Diamond_p/Cu composites prepared at the optimal hot-pressing craft,and the adhesion of the interface between the reinforcement and the matrix is compact.The best properties of SiC_p/Cu composite prepared under the optimal hot-pressing craft are as follows:thermal diffusion 97.962mm²/s,thermal conductivity 270W/（m·K）,coefficient of thermal expansion 9.032ppm,bending strength 177.27Mpa,when the volume of Mo coated SiC particles is about 50%.While,when the volume of Mo coated Diamond particles is about 40%,the Diamond_p/Cu composite prepared under the optimal hot-pressing craft get the best properties:thermal diffusion 205.316mm²/s,thermal conductivity 557.588W/（m·K）,coefficient of thermal expansion 11.881ppm,bending strength 179.18Mpa.Ag powders with good degree of sphericity and particle size were reduced from the silver nitrate using the formaldehyde as the reducer.SiC particles or Diamond particles can be wraped with Ag coating integratedly and meanwhile mixed with the Ag particles evenly using this one step chemical reduction method.The hot-pressing sintering for Ag matrix composites were studied and optimized and the optimal hot-pressing craft is as follows:hot-pressing temperature 750^oC,hot-pressing time 120min,hot-pressing pressure 30Mpa.Prepared under the optimal hot-pressing craft the compactness of the composites will be higher than 98%and the hermeticity can reached the level of 10^-8.The best properties of SiC_p/Ag composite prepared under the optimal hot-pressing craft are as follows:thermal conductivity 288.187W/（m·K）,coefficient of thermal expansion9.322ppm,bending strength 152.788Mpa,when the volume of Mo coated SiC particles is about 50%.While,the Diamond_p/Cu composite prepared under the optimal hot-pressing craft get the best properties as follows:thermal conductivity317.532W/（m·K）,coefficient of thermal expansion 9.642ppm,bending strength150.142Mpa,when the volume of Mo coated Diamond particles is about 50%too.At last,The geometrical thermal conductivity model was designed from one-dimensional to three-dimensional according to Fourier’s law of heat conduction and electric conductivity.In the three-dimensional thermal conductivity model,cube reinforcement model,spheriform reinforcement model and core-shell spheriform reinforcement model were established.Then the calculated formulas were validated according the results of the composites fabricated in this paper and the rules are as follows:when the volume of reinforement is lower than 30%,the change rules of thermal conductivity of the composites can be forecasted exactly by the cube reinforcement model and the spheriform reinforcement model.While the the volume of reinforement is higher than 30%,the change rules of thermal conductivity of the composites can be forecasted exactly by the core-shell spheriform reinforcement model.